1. Field of the Invention
The present invention relates to a head lamp unit for an automobile, and more specfically, to a head lamp used in a 4-lamp system in which two lighting fixtures constitute one lighting fixture unit.
2. Description of the Prior Art
An example of a conventional head lamp unit 90 of the kind mentioned above is shown in FIG. 7. For example, a reflecting mirror 92a and a bulb 92b of one lighting fixture 92 and a reflecting mirror 93a and a bulb 93b of the other lighting fixture 93 are disposed behind a lens 91. The aforementioned one lighting fixture 92 employs a bulb 92b, for example, such as an H4 halogen bulb provided with a filament for a running beam and a filament for a passing beam, whereas the other lighting fixture 93 employs a bulb 93b, for example, such as an Hl halogen bulb provided only with a filament for a running beam.
With this conventional arrangement, when the vehicle runs with the passing beam operative, one lighting fixture 92 is lit whereas the other lighting fixtures 93 is not lit.
In case of the aforesaid passing mode, the light distribution characteristic, in the left-side passing, is asymmetric to the left and right in order to easily read a road sign or the like on the left side of the road. Portions opposite to the lighting fixtures 92 and 93 of the lens 91 are applied with lens cuts corresponding thereto to make adequate the light distribution characteristic of the lighting fixtures 92 and 93.
However, in the conventional head lamp 90 constructed as described above, when the vehicle runs with the passing light beam, lighting becomes unavoidably darker than when running with the running beam. Furthermore, a hood is provided at a lower half portion of the filament for the passing beam to shape the light distribution characteristic so that approximately one half of the light is shielded, which further causes poor illumination. This gives rise to a problem of failing to meet today's traffic circumstances in which running in the passing beam mode is compelled to be choosen during a major portion of night running even on an express road with much traffic. This problem should be solved.
For solving the aforesaid problem, a proposal has been made in which filaments for the passing beam are provided on both of the aforesaid lighting fixtures 92 and 93, respectively. In this case, however, asymmetric light distribution characteristics E1 and E2 become doubled, as shown in FIG. 8. It becomes extremely difficult to arrange the respective light distributions E1, E2 to meet each other to provide trouble-free light distribution characteristics in practical use. Thus, this arrangement fails to constitute a satisfactory solution to the problem.